Quick Rochester Quadrajet Question- CFM/flow

[Bigprairie1]

As a few of you know I am set to do some tuning on the Rochester Quadrajet I have on my recently acquired '72 Chev, many thanks for the info on that by the way.
I have another question regarding this carb that some of you might have some insight into:
Any idea as to how much CFM flow these carbs provided?
I googled the carb model (7042210) and the info varied all the way up to 750 CFM...which I find a bit hard to believe.
Again the carb is original to the truck and motor (72' 350-4bbl/4 bolt truck- 1/2 ton).
Any info you guys might have would be, again, much appreciated.
Thanks!!
BP

 

[rbh]

Re: Quick Rochester Quadrajet Question- CFM/flow

I was always told that a 650 flows 650 cfm and a 750 flows 750 cfm, but the only true way to make sure is to put it on a flow bench.

 

[dolluper]

Re: Quick Rochester Quadrajet Question- CFM/flow

Ouads were up in the 750 range....you want the specs and manual freebie go here link below ...right side see chev trucks PDF files enjoy...should keep you busy LOL's
http://www.newagemetal.com/

 

[Don S]

Re: Quick Rochester Quadrajet Question- CFM/flow

Think you're confused now, look at this site.
http://www.florida4x4.com/tech/quadrajet/index.php

 

[stackz]

Re: Quick Rochester Quadrajet Question- CFM/flow

if its the original carb, its likely a 600/650cfm model.

where did you pull the carb numbers from? the base plate or the carb throat? were there any numbers over by the choke at all on the body?

have you had it apart yet so you could look at the jet numbers? If you have a set of calipers you can measure the throttle bores to get better sizing and then cross reference against known quads.

I personally have always hated the q-jet carbs and toss them in favor of holleys and edelbrocks but thats just me.

 

[mkast]

Re: Quick Rochester Quadrajet Question- CFM/flow

Ouads were up in the 750 range....

I think a number 1910 flowed 850 cfm.

 

[Bigprairie1]

Re: Quick Rochester Quadrajet Question- CFM/flow

if its the original carb, its likely a 600/650cfm model.

where did you pull the carb numbers from? the base plate or the carb throat? were there any numbers over by the choke at all on the body?

have you had it apart yet so you could look at the jet numbers? If you have a set of calipers you can measure the throttle bores to get better sizing and then cross reference against known quads.

I personally have always hated the q-jet carbs and toss them in favor of holleys and edelbrocks but thats just me.

I got the numbers from the right (drivers) side just about the throttle shaft. They are punch in a vertical fashion on the carb body to the right of the 'Quadrajet' signage.
The numbers (7042210) are correct for the truck and motor according to all the GM literature I have. (ie: '72 Chev/1/2 ton/350-automatic).
I haven't had it apart yet but I've started to clean it up a bit. As well, I'm going to take a look at the choke system (including 'pull off') to make sure all of that is set properly. It currently is a little 'cold natured' on start-up.
I was told that the Quadrajet seals dried out quite a bit...particularly on the southern trucks, which this one is.
I've thought about moving to an Edelbrock carb/manifold system to get a little better performance...but first things first.
All Good
BP

 

[tschmidty]

Re: Quick Rochester Quadrajet Question- CFM/flow

Quadrajets can be a pain to set up but they do get better gas mileage than Holley/Edelbrocks. If you care about the sort of thing. I do like getting double digits in my Firebird 400. Tuned well they run great but as I said they can be a pain.

 

[j_martin]

Re: Quick Rochester Quadrajet Question- CFM/flow

I've run several large vans of that vintage (when I had 9 kids at home). Some came with a quadrajet on em, and some a thermoquad. When I got done setting them up, they all had quadrajets.

Set up right, the secondaries never opened under normal driving conditions. When some jerk kid playing leapfrog with a ford pickup finally po'd me enough to floor it, I swear I could see the top of the doghouse dish in, and the noise scared my kids. Ford saw taillights.

Love that carb. Simple, but effective.

 

[RogersJetboat454]

Re: Quick Rochester Quadrajet Question- CFM/flow

As a few of you know I am set to do some tuning on the Rochester Quadrajet I have on my recently acquired '72 Chev, many thanks for the info on that by the way.
I have another question regarding this carb that some of you might have some insight into:
Any idea as to how much CFM flow these carbs provided?
I googled the carb model (7042210) and the info varied all the way up to 750 CFM...which I find a bit hard to believe.
Again the carb is original to the truck and motor (72' 350-4bbl/4 bolt truck- 1/2 ton).
Any info you guys might have would be, again, much appreciated.
Thanks!!
BP

If I remember correctly most of the Q-jet bodies were capable of flowing 750 CFM. What limited the CFM to less was the tab length on the arm (vacuum pod rod connects to it) of the secondary air valve. You can file this tab down so the secondary air valve opens all the way up which would make it a 750 CFM carb, but unless your turning 8000 RPM, why would you need a 750 CFM carb on a SBC? Bigger isn't always better.

With the proper tuning this carb will be just as good if not better than a Holley or Carter style carb. It's triple venturies in the primarys are an advantage the other carbs don't have (think better fuel atomization which leads to better throttle response and more MPG). It can be a P.I.T.A. to set up, but totally worth it.

 

[Bigprairie1]

Re: Quick Rochester Quadrajet Question- CFM/flow

Again, such great info and experience on this sight really sheds light on this kind of stuff.
I have 2 spare Quadrajet carbs...almost identical to the original one on the truck. They are slightly different applications wherein one is the original off a '71 3/4ton 350-4bbl/auto and the other is off a '72 1/2 ton 350-4bbl/auto NON-California. The one currently on the truck is the one that came with the California emission package (including the ol' A.I.R air pump) system.
I have priced out a couple of 'carb kits' and they are about $30 each and they differ on the two carbs I just mentioned. I think I will try to rebuild one of these things 'off line' while running the truck with the carb that is on it and see how it all works out.
The '72 GM truck service manual gets into the carb rebuild stuff....so combined with that and some of the youtube links, it might just be a successful undertaking???
You guys know your stuff and it's much appreciated!!!
BP

 

[dolluper]

Re: Quick Rochester Quadrajet Question- CFM/flow

You are vary close to the lean drop year of quads...investagate.....old mem.....says 73.....check her out......choke housing gasket was troublesome ......and power booster carb connection lossened.....vac leaks

 

[Bigprairie1]

Re: Quick Rochester Quadrajet Question- CFM/flow

You are vary close to the lean drop year of quads...investagate.....old mem.....says 73.....check her out......choke housing gasket was troublesome ......and power booster carb connection lossened.....vac leaks

...interesting. Any more info on this dolluper as to how I would know? I know GM changed a lot of stuff in '73 from body styles to increased emissions.
Power booster carb connection....do you mean Brake Booster? On this carb it attaches directly to the back of the carb, not the intake manifold like some other Quadrajets...and I did tighten it but that doesn't mean it isn't leaking.
What would the net result be if it was a 'lean drop' quadrajet in overall circumstance?
(noting I also have '71 Quadrajet off a 350-4bbl 3/4ton...nothing like spares!!)
I have more questions to come on this whole truck project...all good stuff tho'.
Many Thanks
BP

 

[dolluper]

Re: Quick Rochester Quadrajet Question- CFM/flow

Thats right the solid piping to the brake booster....the link I posted should give the settings for your model#carb....just check and see if it calls for a lean drop after setting the screws...I think it isn't a lean dropper....heres a link to PDF file for tunning and jet sizes ,rod sizes
http://www.corvetteclub.org.uk/files/downloads/how_to_tune_a_qjet.pdf